1. Field of the Invention
The invention relates to a semiconductor process, and in particular to a structure and method of manufacturing single-crystal silicon carbide/single-crystal silicon heterojunctions with negative differential resistance characteristics.
2. Description of Related Art
Since tunnel diode and Gunn diode were developed, negative differential resistance occurring at a P-N junction and in bulk semiconductors has widely drawn attention. Structures with N-type and S-type negative differential resistance (NDR) have been applied to manufacture high-speed switches, high-frequency oscillators or A/D converters. In addition, with their potential of being able to greatly reduce the complexities of multiple-value logic circuits, many NDRs are widely used to develop and manufacture memory cells and multi-stable switches. In the past, Group III-V negative differential resistance devices have been applied to research and develop high-speed switches, high-frequency oscillators or A/D converters, wherein a portion of devices having the characteristics of multiple negative differential resistance (MNR) can significantly reduce the complexities of multiple-valued logic circuits. Therefore, they can also be widely used for developing and manufacturing memory cells, A/D converters and multi-stable switches. Currently, most negative differential resistance devices are Group III-V semiconductor devices, such as resonant tunneling devices and double-heterojunction optical electrical switches. In addition, these devices can be used in advanced circuits, such as high-frequency oscillators and enhanced-logic circuits with photoelectric characteristics. However, since related processes are quite complicated, difficult and are not compatible with the processes of silicon integrated circuits, manufacturing costs are higher, and these devices can not work at temperatures over 200.degree. C. Therefore, there are certain limitations for some special applications. Small portion of devices with negative differential resistance are manufactured with amorphous silicon. However, these devices have the disadvantages of low peak-to-valley current ratio (PVCR) and low reproducibility. Furthermore, they can not work at high temperatures.